Indian police take Ashok Kumar, a schoolbus attendant accused of murdering a pupil at Ryan International School in Gurgaon, to court on September 12, 2017. Sanjeev Verma / Hindustan Times via Getty Images

The crime was horrific: a 7-year-old boy's throat slashed at school just minutes after his father dropped him off. But the investigations that followed have also highlighted the tendency of Indian police to use the poor as scapegoats when under pressure to solve cases.

The body of Pradyuman Thakur was found near a toilet at the Ryan International School in the town of Bhondsi, near Delhi, on the morning of September 8. Within hours, police had identified the killer as Ashok Kumar, a conductor on one of the school’s buses. He was arrested the same evening.

Police said Mr Kumar, 42, took a knife to the toilet to clean it and, seeing Pradyuman there, tried to sexually assault him before killing him.

“The CCTV footage clearly shows his presence inside the toilet and eyewitness accounts match the sequence of events,” Sumit Kuhar, the deputy commissioner of the local police, said on September 9. “We have strong circumstantial evidence to prove his guilt in court.”

Police also claimed that their investigations had uncovered a history of sexually predatory behaviour by Mr Kumar.

But Barun Thakur, the victim's father, insisted that the police had acted in haste and demanded a probe by the Central Bureau of Investigation (CBI), a federal agency. State authorities agreed after Mr Thakur threatened to petition the supreme court for the CBI’s involvement.

The CBI began its investigation on September 22. On November 8, the agency detained a 16-year-old student of the school as its primary suspect, based on both “material evidence” and a confession. The teenager — who cannot be named because he is a juvenile — had anger management issues and had been struggling in his studies, the CBI said.

He “wanted to have an examination and a parent-teacher meeting postponed”, and Pradyuman was a random target killed just to disrupt the school’s schedules, a CBI spokesman said on Wednesday.

The police issued a response to the CBI's findings on Friday, arguing that the investigation had been taken away from them before they could complete it.

"I admit there were some loopholes in the probe," said Sandip Khirwar, police commissioner for Gurgaon district where the school is located.

On Thursday and Friday, in an attempt to re-enact the crime, the CBI took the teenager to knife shops in the town to establish where the murder weapon was purchased. At the school he was asked to demonstrate on a dummy how he had killed Pradyuman, in an attempt to corroborate his knowledge with forensic evidence.

The teenager’s father said his son was forced to make a confession. “My son was tortured, beaten, hung upside-down, and his head submerged into water by CBI investigators to obtain a confession,” he told reporters on Saturday at a hearing in a juvenile justice court. “My son is being framed by the agency.”

He did not however make this claim in court.

The CBI told the court that the student confessed to the murder in the presence of his father and other independent witnesses including a social worker.

The court ordered the student to be held at a correctional facility in Faridabad, another Delhi suburb, until the next hearing on November 22.

Despite the CBI's findings, Mr Kumar remains in prison, awaiting a hearing of his bail plea on November 16. His lawyer, Mohit Verma, said the bus conductor plans to sue the police as well as the school’s authorities for “large-scale defamation”.

Mr Verma said other members of the school’s staff, such as a gardener and the driver of Mr Kumar’s bus, were pressured by police to implicate him. He said the police took thumb impressions from his client, who is illiterate, on a blank sheet of paper, to append to a written confession. Mr Kumar was also beaten and drugged during the investigation, the lawyer said.

“The police planted everything. They framed an innocent man," Mr Verma said. “Who pressurised police to do that is a matter for investigation. But whatever happened to Ashok amounts to torture.”

The kind of mistreatment alleged by Mr Kumar has been noted in a Human Rights Watch report on India’s police, released in 2009.

“Individuals who are poor and socially or politically marginalised are especially vulnerable to prolonged detention and repeated ill-treatment,” the report said.

The police "use illegal detention, torture and ill-treatment to punish criminals against whom they lack the time or inclination to build cases, or to elicit confessions, even ones they know are false”.

No statistics are maintained for the number of wrongful arrests made by police.

M S Sharma, a Delhi lawyer who often represents poor defendants for free in criminal cases, said the police resort to such abuses because of pressure to produce quick results, particularly in high-profile cases.

One such case is the September 2006 bombings in Malegaon, not far from Mumbai, in which dozens of people were killed. Police arrested nine Muslim men in the following months, none of whom could afford a lawyer. But with legal assistance provided by a non-profit organisation, all nine were acquitted in April last year.

Police officers are also prejudiced against the poor, believing they are more likely to commit crimes, Mr Sharma said. And because they have no influence or money for legal representation, they can be tortured to confess without fear of repercussions.

The result, he said, is that “the lives of innocent men and women are destroyed for no reason”.